AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

A Forward Stratigraphic Model of Fluvial Meander Evolution, Point-Bar Facies Architecture and Heterogeneity: Subsurface Applications

Abstract

Sinuous, meandering, channels characterize the lower reaches of many fluvial systems. Although fundamental types of meander-bend transformations have been recognized (expansion, translation, rotation, and combinations thereof), the relationships between the migratory behavior of a river and the geometry and lithofacies organization of deposits that arise from channel migration (e.g., point bars, counter point-bars) are poorly understood. Stratigraphic successions of fluvial depositional elements are commonly characterized by vertical and lateral facies heterogeneity that is indicative of highly variable mechanisms of accretion. Sand-prone packages are draped and partitioned by mud-prone deposits of variable thickness and continuity. Furthermore, at a larger scale, the morphology and preserved lithofacies of meander belts is influenced by both autogenic factors, such as frequency of nodal avulsion, and allogenic factors, such as climate-driven changes in sediment delivery and the role of differential subsidence in controlling direction and rate of meander-belt migration. As empirical equations and hydro-morphological relations have inherent limitations due to the complexity of channel patterns in natural streams, a forward stratigraphic model has been developed here that uses a combined geometric-stochastic approach. The model is able to replicate bar-growth trajectories and sedimentary structures of meandering systems based on real-world data of sedimentary architecture derived from modern rivers and ancient successions that serve as geologic analogs. The model can be used to provide linkage between local outcrop measurements and large-scale evolutionary behavior; it allows quantitative assessments of possible scenarios depicted in traditional qualitative facies models. The 3D realization of modeling outputs can be employed to condition reservoir-modeling efforts at different spatial scales, in particular through the creation of training images for constraining reservoir models built through techniques based on Multi-Point Statistics. The 3D modelling outputs also assist the investigation of the sensitivity of dynamic reservoir connectivity to different styles of meander-belt architecture, from the bar scale to the scale of amalgamated meander belts. Furthermore, the model can be applied to inform flow-based up-scaling, and enables prediction of analogous subsurface fluvial architectures from the history and timing of basin-bounding-fault movement.